Cosmic Rays can Help Keep the World's Clocks in Sync

The world has a robust, accurate timekeeping system that regulates our clocks. Humanity uses it for everything we do, from our financial systems to satellite navigation, computer and phone networks, and GPS. But the current system is not perfect, and has vulnerabilities to cyber-attack and disruption. Given the importance of accurate timekeeping to our society (as a fundamental underpinning of life in the 21st century), experts are always looking for ways to improve the system and add redundancy. Researchers at the University of Tokyo have taken a big step in this direction, developing a new method of time synchronization that takes advantage of cosmic rays to calibrate the world’s clocks.

There are two big challenges in timekeeping. The first is keeping a clock accurate over a long period of time. Humans have gotten progressively better at this over the centuries, from ancient water clocks to mechanical pendulum-driven grandfather clocks in the nineteenth century. Modern timepieces largely work using the rhythmic vibrations of quartz crystals, though even these fail to match the accuracy of atomic clocks, which keep time by taking advantage of the fact that the energy required to change the orbit of an electron around an atom is consistent across the Universe. With these atomic measurements, the latest and greatest atomic clocks only lose about one second every ten million years.

But the second – and arguably more difficult challenge in timekeeping – is making sure multiple clocks around the world agree with one another. Clocks aboard satellites in orbit, like those we use for GPS, need to be regularly calibrated from ground-based atomic clocks to work consistently (and, they have to take time dilation into account, as time moves differently in orbit than it does down here in Earth’s gravity well. Thanks Einstein!) It is this synchronization problem that Professor Hiroyuki Tanaka at the University of Tokyo hopes to improve with a new method.

The Cosmic Time System (CTS) prototype is a small, lightweight device that can synchronize with similar devices by measuring muon particles from cosmic rays. Credit: ©2022 Hiroyuki K. M. Tanaka

Tanaka calls the method CTS, which stands for Cosmic Time System, and it relies on sensors that detect particles left over from the collision of cosmic rays with Earth’s atmosphere. The cosmic rays are scattered at an altitude of about fifteen kilometers up, causing a shower of particles, some of which reach the ground, including muons traveling near the speed of light. CTS devices in multiple locations can detect these muons and use them to synchronize with each other. Each muon shower has its own unique signature, enabling CTS devices to identify a singular event and sync up to one another based on that event.

Muons penetrate through rock and water, meaning these devices would work inside buildings, in submarines, and in underground train tunnels. “Satellite-based time synchronization has so many blind spots at the poles, in mountainous regions or underwater” said Tanaka, “and CTS could fill these gaps and more.”

 Muon showers caused by particles slamming into the Earth’s atmosphere can be used to synchronize clocks, even deep underground. Credit: ©2022 Hiroyuki K. M. Tanaka

And because these are naturally occurring signals, they cannot be interfered with or hacked like artificial GPS signals.

Tanaka believes that CTS could revolutionize the way timekeeping works, and also perhaps navigation too. “It’s relatively easy to keep time accurately these days. For example, atomic clocks have been doing this for decades now,” said Tanaka. “However, these are large and expensive devices that are very easy to disrupt. This is one reason I have been working on an improved way to keep time. The other is that, related to time measurement, position measurement could also be made better. So really, CTS is a precursor to a potential replacement for GPS, but that’s still a little further down the line.”

Learn More:

“Keeping time with the cosmos: A new method to synchronize devices on Earth makes use of cosmic rays” University of Tokyo.